Arindam P. Ghosh

CHOP Potentially Co-Operates with FOXO3a in Neuronal Cells to Regulate PUMA and BIM Expression in Response to ER Stress

Endoplasmic reticulum (ER) stress-induced apoptosis has been implicated in various neurodegenerative diseases including Parkinson Disease, Alzheimer Disease and Huntington Disease. PUMA (p53 upregulated modulator of apoptosis) and BIM (BCL2 interacting mediator of cell death), pro-apoptotic BH3 domain-only, BCL2 family members, have previously been shown to regulate ER stress-induced cell death, but the upstream signaling pathways that regulate this response in neuronal cells are incompletely defined. Consistent with previous studies, we show that both PUMA and BIM are induced in response to ER stress in neuronal cells and that transcriptional induction of PUMA regulates ER stress-induced cell death, independent of p53. CHOP (C/EBP homologous protein also known as GADD153; gene name Ddit3), a critical initiator of ER stress-induced apoptosis, was found to regulate both PUMA and BIM expression in response to ER stress. We further show that CHOP knockdown prevents perturbations in the AKT (protein kinase B)/FOXO3a (forkhead box, class O, 3a) pathway in response to ER stress. CHOP co-immunoprecipitated with FOXO3a in tunicamycin treated cells, suggesting that CHOP may also regulate other pro-apoptotic signaling cascades culminating in PUMA and BIM activation and cell death. In summary, CHOP regulates the expression of multiple pro-apoptotic BH3-only molecules through multiple mechanisms, making CHOP an important therapeutic target relevant to a number of neurodegenerative conditions.

l-2-Hydroxyglutarate: An Epigenetic Modifier and Putative Oncometabolite in Renal Cancer

UNLABELLED Through unbiased metabolomics, we identified elevations of the metabolite 2-hydroxyglutarate (2HG) in renal cell carcinoma (RCC). 2HG can inhibit 2-oxoglutaratre (2-OG)-dependent dioxygenases that mediate epigenetic events, including DNA and histone demethylation. 2HG accumulation, specifically the d enantiomer, can result from gain-of-function mutations of isocitrate dehydrogenase (IDH1, IDH2) found in several different tumors. In contrast, kidney tumors demonstrate elevations of the l enantiomer of 2HG (l-2HG). High-2HG tumors demonstrate reduced DNA levels of 5-hydroxymethylcytosine (5hmC), consistent with 2HG-mediated inhibition of ten-eleven translocation (TET) enzymes, which convert 5-methylcytosine (5mC) to 5hmC. l-2HG elevation is mediated in part by reduced expression of l-2HG dehydrogenase (L2HGDH). L2HGDH reconstitution in RCC cells lowers l-2HG and promotes 5hmC accumulation. In addition, L2HGDH expression in RCC cells reduces histone methylation and suppresses in vitro tumor phenotypes. Our report identifies l-2HG as an epigenetic modifier and putative oncometabolite in kidney cancer. SIGNIFICANCE Here, we report elevations of the putative oncometabolite l-2HG in the most common subtype of kidney cancer and describe a novel mechanism for the regulation of DNA 5hmC levels. Our findings provide new insight into the metabolic basis for the epigenetic landscape of renal cancer.

Lysosome Dysfunction Triggers Atg7-dependent Neural Apoptosis

Macroautophagy (autophagy) is a process wherein bulk cytosolic proteins and damaged organelles are sequestered and degraded via the lysosome. Alterations in autophagy-associated proteins have been shown to cause neural tube closure defects, neurodegeneration, and tumor formation. Normal lysosome function is critical for autophagy completion and when altered may lead to an accumulation of autophagic vacuoles (AVs) and caspase activation. The tumor suppressor p53 is highly expressed in neural precursor cells (NPCs) and has an important role in the regulation of both autophagy and apoptosis. We hypothesized that altered lysosome function would lead to NPC death via an interaction between autophagy- and apoptosis-associated proteins. To test our hypothesis, we utilized FGF2-expanded NPCs and the neural stem cell line, C17.2, in combination with the lysosomotropic agent chloroquine (CQ) and the vacuolar ATPase inhibitor bafilomycin A1 (Baf A1). Both CQ and Baf A1 caused concentration- and time-dependent AV accumulation, p53 phosphorylation, increased damage regulator autophagy modulator levels, caspase-3 activation, and cell death. Short hairpin RNA knockdown of Atg7, but not Beclin1, expression significantly inhibited CQ- and Baf A1-induced cell death, indicating that Atg7 is an upstream mediator of lysosome dysfunction-induced cell death. Cell death and/or caspase-3 activation was also attenuated by protein synthesis inhibition, p53 deficiency, or Bax deficiency, indicating involvement of the intrinsic apoptotic death pathway. In contrast to lysosome dysfunction, starvation-induced AV accumulation was inhibited by either Atg7 or Beclin1 knockdown, and Atg7 knockdown had no effect on starvation-induced death. These findings indicate that Atg7- and Beclin1-induced autophagy plays a cytoprotective role during starvation but that Atg7 has a unique pro-apoptotic function in response to lysosome dysfunction.

Cytoplasmic p53 and Activated Bax Regulate p53-dependent, Transcription-independent Neural Precursor Cell Apoptosis

The prodeath effects of p53 are typically mediated via its transcriptional upregulation of proapoptotic Bcl-2 family members, including PUMA, Noxa, and/or Bax. We previously reported that staurosporine (STS), a broad-spectrum kinase inhibitor and prototypical apoptosis-inducing agent, produced p53-dependent, Bax-dependent, neural precursor cell (NPC) apoptosis, but that this effect occurred independently of new gene transcription and PUMA expression. To further characterize the mechanism by which p53 regulates NPC death, we used primary cerebellar NPCs derived from wild-type, p53-deficient, and Bax-deficient neonatal mice and the mouse cerebellar neural stem cell line, C17.2. We found that STS rapidly increased p53 cytoplasmic immunoreactivity in neuritic-like processes in C17.2 cells, which preceded Bax activation and caspase-3 cleavage. Confocal microscopy analysis of STS-treated cells revealed partial colocalization of p53 with the mitochondrial marker pyruvate dehydrogenase as well as with conformationally altered “activated” Bax, suggesting an interaction between these proapoptotic molecules in triggering apoptotic death. Nucleophosmin (NPM), a CRM1-dependent nuclear chaperone, also exhibited partial colocalization with both activated Bax and p53 following STS treatment. These observations suggest that cytoplasmic p53 can trigger transcription-independent NPC apoptosis through its potential interaction with NPM and activated Bax.

The proapoptotic BH3-only, Bcl-2 family member, Puma is critical for acute ethanol-induced neuronal apoptosis.

Synaptogenesis in humans occurs in the last trimester of gestation and in the first few years of life, whereas it occurs in the postnatal period in rodents. A single exposure of neonatal rodents to ethanol during this period evokes extensive neuronal apoptosis. Previous studies indicate that ethanol triggers the intrinsic apoptotic pathway in neurons, and that this requires the multi-BH domain, proapoptotic Bcl-2 family member Bax. To define the upstream regulators of this apoptotic pathway, we examined the possible roles of p53 and a subclass of proapoptotic Bcl-2 family members (i.e. the BH3 domain-only proteins) in neonatal wild-type and gene-targeted mice that lack these cell death inducers. Acute ethanol exposure produced greater caspase-3 activation and neuronal apoptosis in wild-type mice than in saline-treated littermate controls. Loss of p53-upregulated mediator of apoptosis (Puma) resulted in marked protection from ethanol-induced caspase-3 activation and apoptosis. Although Puma expression has been reported to be regulated by p53, p53-deficient mice exhibited a similar extent of ethanol-induced caspase-3 activation and neuronal apoptosis as wild-type mice. Mice deficient in other proapoptotic BH3-only proteins, including Noxa, Bim, or Hrk, showed no significant protection from ethanol-induced neuronal apoptosis. Collectively, these studies indicate a p53-independent, Bax- and Puma-dependent mechanism of neuronal apoptosis and identify Puma as a possible molecular target for inhibiting the effects of intrauterine ethanol exposure in humans.

bcl-2/Adenovirus E1B 19-kd interacting protein 3 (BNIP3) regulates hypoxia-induced neural precursor cell death.

Perinatal hypoxia-ischemia may result in long-term neurological deficits. In addition to producing neuron death, HI causes death of neural precursor cells (NPCs) in the developing brain. To characterize the molecular pathways that regulate hypoxia-induced death of NPCs, we treated a mouse neural stem cell line (C17.2 cells) and fibroblastic growth factor II-expanded primary NPCs derived from wild-type or gene-disrupted mice, with oxygen glucose deprivation or the hypoxia mimetics desferrioxamine or cobalt chloride. Neural precursor cells undergoing hypoxia exhibited time- and concentration-dependent caspase-3 activation and cell death, which was significantly reduced by treatment with a broad caspase inhibitor or protein synthesis inhibition. Bax/Bak-deficient NPCs were protected from desferrioxamine-induced death and exhibited minimal caspase-3 activation. Oxygen glucose deprivation or hypoxia-mimetic exposure also resulted in increased hypoxia-inducible factor &agr; and bcl-2/adenovirus E1B 19-kd interacting protein 3 (BNIP3) expression. BNIP3 shRNA treatment failed to affect hypoxia-induced caspase-3 activation but inhibited cell death and nuclear translocation of apoptosis-inducing factor, indicating that BNIP3 is an important regulator of caspase-independent NPC death after hypoxia. These studies demonstrate that hypoxia activates both caspase-dependent and -independent NPC death pathways that are critically regulated by multiple Bcl-2 family members.

Deficiency of Pro-apoptotic Hrk Attenuates Programmed Cell Death in the Developing Murine Nervous System but Does Not Affect Bcl-x Deficiency-Induced Neuron Apoptosis

The BCL-2 family includes both pro- and anti-apoptotic proteins, which regulate programmed cell death during development and in response to various apoptotic stimuli. The BH3-only subgroup of pro-apoptotic BCL-2 family members is critical for the induction of apoptotic signaling, by binding to and neutralizing anti-apoptotic BCL-2 family members. During embryonic development, the anti-apoptotic protein BCL-XL plays a critical role in the survival of neuronal populations by regulating the multi-BH domain protein BAX. In this study, the authors investigated the role of Harakiri (HRK), a relatively recently characterized BH3-only molecule in disrupting the BAX-BCL-XL interaction during nervous system development. Results indicate that HRK deficiency significantly reduces programmed cell death in the nervous system. However, HRK deficiency does not significantly attenuate the widespread apoptosis seen in the Bcl-x−/− embryonic nervous system, indicating that other BH3-only molecules, alone or in combination, may regulate BAX activation in immature neurons.

Kinomic profiling identifies focal adhesion kinase 1 as a therapeutic target in advanced clear cell renal cell carcinoma

The introduction of targeted therapies has caused a paradigm shift in the treatment of metastatic clear cell (cc)-renal cell carcinoma (RCC). We hypothesized that determining differential kinase activity between primary and metastatic tumor sites may identify critical drivers of progression and relevant therapeutic targets in metastatic disease. Kinomic profiling was performed on primary tumor and metastatic tumor deposits utilizing a peptide substrate microarray to detect relative tyrosine phosphorylation activity. Pharmacologic and genetic loss of function experiments were used to assess the biologic significance of the top scoring kinase on in vitro and in vivo tumor phenotypes. Kinomics identified 7 peptides with increased tyrosine phosphorylation in metastases that were significantly altered (p<0.005). Based on these peptides, bioinformatics analyses identified several candidate kinases activated in metastases compared to primary tumors. The highest ranked upstream kinase was Focal Adhesion Kinase 1 (FAK1). RCC lines demonstrate evidence of elevated FAK1 activation relative to non-transformed renal epithelial cells. Pharmacologic inhibition of FAK1 with GSK2256098 suppresses in vitro tumor phenotypes. In turn, FAK1 knockdown in RCC cells suppresses both in vitro phenotypes and in vivo tumor growth. Collectively, these data demonstrate functional activation of FAK1 in metastases and provide preclinical rationale for targeting this kinase in the setting of advanced ccRCC.

Genetics of renal cancer: focus on MTOR.

Renal cell carcinoma (RCC) has multiple subtypes and may occur in hereditary and sporadic forms. Sporadic renal cell carcinomas are most commonly clear cell cancers (80%). Metastatic disease is found at presentation in almost 30% of patients with renal cell carcinoma and treatment of RCC metastases is greatly different from the treatment regimens of the primary tumor. Currently, several FDA approved therapies exist for metastatic clear cell RCC (ccRCC) which includes two rapamycin analogs-everolimus and temsirolimus. The mammalian target of rapamycin (mTOR) is a serine/threonine kinase and catalytic subunit of two biochemically distinct complexes called mTORC1 and mTORC2. Recently published TCGA data report aberrations in the PI3K/AKT/mTOR pathway in up to 28% of RCC cases [1]. Whether these aberrations predict for clinical benefit of mTOR-targeted therapy in ccRCC patients is debatable. Prior studies have identified hyperactivating point mutations in mTOR that remain sensitive to rapamycin [2] while other recent studies have identified a somatic mutation in mTOR that is resistant to allosteric mTOR inhibition while remaining sensitive to mTOR kinase inhibitors [3]. Mutations in MTOR are clustered in various regulatory domains in ccRCC. We focused our attention on a prominent cluster of hyperactivating mutations in the FAT (FRAP–ATM–TTRAP) domain of mTOR in ccRCC that led to an increase in both mTORC1 and mTORC2 activities and led to an increased proliferation of cells [4]. Several of the FAT domain mutants demonstrated a decreased binding of the intrinsic inhibitor DEPTOR (DEP domain containing mTOR-interacting protein), while a subset of these mutations showed altered binding of the negative regulator PRAS40 (proline rich AKT substrate 40). We also identified a recurrent mutation in RHEB (Ras homolog enriched in brain) in ccRCC patients that exclusively increased mTORC1 activity. Interestingly, mutations in the FAT domain of MTOR and in RHEB remained sensitive to rapamycin, though several of these mutations demonstrated residual mTOR kinase activity after treatment with rapamycin at clinically relevant doses. Overall, our data suggests that point mutations in the mTOR pathway may lead to downstream mTOR hyperactivation through multiple different mechanisms to confer a proliferative advantage to a tumor cell. Given the central role of mTORC1 as a downstream target of PI3K activity, there exists a clear rationale for targeting mTORC1 in cancer and using rapalogs clinically. Unfortunately, the effectiveness of rapamycin as a single agent therapy is fraught with several limitations. mTORC1 promotes IRS-1 degradation [5] implying that the potential therapeutic benefit of inhibiting mTORC1 with rapamycin is opposed by the release of feedback inhibition of PI3K/AKT activation. In addition to inhibition of the feedback loop that restrains PI3K/AKT activation, everolimus treatment in breast cancer patients can increase ERK activation by a mechanism which is largely unknown, thereby adding a new level of complexity to allosteric inhibition of mTORC1 by rapalogs [5]. In an attempt to target the mTOR pathway more effectively, novel ATP competitive inhibitors that act at its catalytically active site are being developed. Active-site inhibitors have indeed proved more effective inhibitors of cell proliferation than rapamycin in a variety of tumor subtypes in vitro as they have a distinct advantage in that they inhibit 4E-BP1 phosphorylation at rapamycin resistant sites and also block AKT phosphorylation at Ser473 [6]. Significant homology in the kinase domains of PI3K and mTOR has made possible the development of dual active-site inhibitors. While these agents can circumvent the activation of PI3K/AKT feedback loops activated by rapalogs, dual PI3K/mTOR inhibitors could lead to activation of alternative compensatory pathways. The elucidation of the feedback loops that regulate the outputs of signaling networks is an area of fundamental importance for the rationale design of effective anticancer drugs that can be used in conjunction with PI3K/AKT/mTOR inhibitors. While most of mTOR targeted therapies including everolimus and temsirolimus target mTORC1, mTORC2 is emerging as a pivotal player in many cancers. Defining mTORC2s role in the cellular milieu has been more challenging compared to mTORC1 because of its insensitivity to acute rapamycin treatment. As mTORC2 is a key regulator of cell proliferation and metabolic reprogramming of tumor cells [7], there is an increasing need to design therapeutic agents that specifically target mTORC2. Our in vitro data suggests that these hyperactivating mutations confer relative resistance to rapalog therapy and these findings may have dosing implications for patients with ccRCC. These findings may be highly relevant from a clinical point of view, as MTOR mutations could serve as biomarker predicting tumor responses to mTOR allosteric inhibitors and explain acquired resistance to this class of drugs in humans.

Abstract LB-131: Elevated (L) -2-hydroxyglutarate promotes loss of 5-hydroxymethylcytosine in clear cell renal cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA We undertook an unbiased metabolomics profile of clear cell renal cell carcinoma (ccRCC), the most common histological subtype, to gain deeper insight into the metabolic basis of this disease. Here, we demonstrate elevations of the metabolite 2-hydroxyglutarate (2HG) in kidney cancer. Elevation of 2HG, specifically the D- enantiomer, has been linked to transformation and identified in the context of gain of function mutations of isocitrate dehydrogenase (IDH1 and IDH2). Notably, enantiomeric resolution demonstrates that, in contrast to IDH1/IDH2 mutant tumors, kidney tumors demonstrate elevations of the L enantiomer of 2HG (L-2HG). Moreover, high 2HG tumors demonstrate reduced DNA levels of 5-hydroxymethylcytosine (5hmC) consistent with the ability of L-2HG to inhibit TET (Ten Eleven Translocation) enzymes which convert 5-methylcystoine to 5-hmC. Finally, we demonstrate that these changes are mediated by the reduced expression of L-2HG dehydrogenase (L2HGDH) in ccRCC. Here, we report elevations of the putative oncometabolite L-2HG in the most common subtype of kidney cancer and describe a novel mechanism for the regulation of DNA 5hmC levels. Our findings provide new insight into the metabolic basis for the epigenetic landscape of renal cancer. Citation Format: Eun-Hee Shim, Carolina B. Livi, John Knight, Ross P. Holmes, Dinesh Rakheja, Sadanan Velu, Eun-Young Kho, Balachandra Chenna, Shane L. Rea, Daniel Benson, Richard Kirkman, Arindam Ghosh, Qiuhua Li, Sejong Bae, Shi Wei, Karen L. Block, Sunil Sudarshan. Elevated (L) -2-hydroxyglutarate promotes loss of 5-hydroxymethylcytosine in clear cell renal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-131. doi:10.1158/1538-7445.AM2014-LB-131